The initial prospecting work is conducted on the potential place and consists in taking samples. The first samples are grab as single pieces and later can be composited if were necessary in nature, lacking any definite width characteristics, but useful in identifying local mineralization and possible geochemically anomalous zones. The rock sampling can be done by regular people, but ideally a geologist must oversee this task. It is important to determine sample station using handheld GPS devices, usually accurate to within 5-10 m. As was mentioned samples are initially grab in nature, but also, it is important to take chip samples across structures and veins in order to determine widths of mineralization and the presence of any wall rock mineralization near to these structures.
If the sampling program is detailed, the initial number of samples is more than 500 and this can be composited according to the first mineralogical assessment. For example, it is good practice to prepare at least 100 composites from grab samples in 1-4 m2 areas along 50 m and spaced lines at 10 m spaced sample locations. The samples can be assayed for several elements if there is not any economical restriction, otherwise the assays must include at least gold and silver. In this way we can know a preliminary distribution of metals. For example, of 100 samples collected the average gold value can be 2 g/t, with 40 samples reporting more than 1 g/t gold. Usually, the silver content is higher than gold content. If other metals were assayed, it is possible to establish a correlation between base metals and precious metals. In some places, local high sulphidation epithermal overprints within a predominantly polymetallic style hydrothermal system.
Taking samples by using a shovel
Other initial information to be obtained is the possible occurrence of anomalous to significant contents of precious metals in the different zones where grab samples were taken. If more information is required, part of the samples can be submitted for Whole Rock Analysis and X-Rays. It must be mentioned that samples usually vary from fresh to altered ores. The results to be obtained can confirm the existence of several populations among different rocks such as volcanic and andesite. Then, we can infer can some rock were formed or derived from the chemical reaction or weathering of other rocks. Essentially, it is possible to establish a preliminary paragenesis of the deposit.
Other points to be sampled are stream sediment. These samples have to be collected in different stations along each drainage and theirs positions can be determined by using a GPS. Results of the survey provide information on potential areas of anomalous base and precious metal values throughout the place. By performing statistical analysis is possible to know what zone or zones are more important and basically the gold and silver distribution.
Soils must not be overlooked. It is important to take collected samples over 2.0 km x 2.0 km areas. Samples can be taken at 40 m station along 150 m spaced grid lines, each line approximately 2 km in length. One more time, sample stations are located using a GPS device. Results of this survey let identify precious metals within the grid area.